In such machines and systems, a film is used in which a reference mark has previously been applied, which is used to help the printed figures/inscriptions to be precisely positioned, and to be read automatically by the packaging apparatuses, in the step in which the film itself is wrapped around the material to complete its packaging.
The feeding of the film to the packaging unit is carried out by a feeding unit provided with two reels for unwinding the material, one of which is alternately at work while on the other the run-out reel is replaced with a new loaded reel, which waits for the reel being unwound to run out. There is thus the problem of joining the tail of the running out material with the head of the new loaded reel, with the latter finally replacing the other as the active reel.
The systems currently known for automatically controlling this so-called “reel change” step are unsatisfactory in speed and reliability, indeed often resulting in stops in production that in turn lead to wastage of product due to problems of centering the printing on the package, welding defects, defective packaging as a result of variations in speed of the film etc.